First of all, lasers of higher repetition rate (average power) and / or shorter pulses can be employed. However, the presented system offers various opportunities for the scalability of the photon flux, which has already been separately investigated in the past. Currently, structures of about 50 nm in size are already detectable, among other factors limited by the low signal-to-noise ratio due to the relatively low brilliance of the plasma. It is based on an almost debris-free, longterm stable laser plasma produced in a gaseous target. We have demonstrated the feasibility of a table-top soft x-ray microscope operating at a wavelength of 2.88 nm. It consists basically of a laser-induced plasma source, an ellipsoidal condenser mirror, a Fresnel zone plate objective, and a back-illuminated CCD camera sensitive for soft x-ray radiation. The setup of the table-top soft x-ray microscope is depicted in Figure 1. It makes use of a nearly debris-free, long-term stable laser-induced plasma source based on a pulsed gas jet. Here, the most compact soft x-ray microscope is presented operating in the “water window” region with monochromatic radiation from Helike nitrogen at a wavelength of 2.88 nm. Especially laser-produced plasmas have already been applied successfully in various fields, ranging from material ablation and structuring to absorption spectroscopy and transmission x-ray microscopy. To enable soft x-ray microscopy for everyday use without waiting times due to limited beam time at large-scale facilities, lab-scale sources based on gas discharge or laser-produced plasmas have been employed. However, until now, such studies are almost exclusively conducted at synchrotron sources providing the necessary high photon flux of short wavelength radiation Using Fresnel zone plates as highly magnifying objectives, spatial resolutions in the range of 10 nm have been achieved. Soft x-ray microscopy using a table-top laser-induced plasma source based on a pulsed gas jetīenefiting from the high absorption contrast between carbon and oxygen, transmission x-ray microscopy in the spectral range of the “water window“ (λ = 2.3 – 4.4 nm) is a powerful tool for the investigation of biological and mineralogical samples.
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